Study Of Deactivation And Regeneration Of K Poisoned SCR Catalysts On Gaseous Elemental Mercury Oxidation

SCR（Selective Catalytic Reduction）system is the main device for removing nitrogen oxides and oxidizing elemental mercury in coal-fired power plants.SCR catalyst is the core of SCR system,whether it can work properly is related to the NOx and mercury removal effects of the entire coal-fired power plant.At present,many power plants replace a certain proportion of biomass into coal as the fuel source.However,the deactivation rate of SCR catalysts will increase in these power plants,which was mainly caused by KCl and K₂SO₄ in flue gas.The study on mercury oxidation by SCR catalysts with KCl and K₂SO₄ deposited on the surface has important guiding significance for the study of anti-K poisoning catalysts and the arrangement of SCR catalyst in coal-fired power plants.In this thesis,deactivation mechanism of KCl and K₂SO₄ poisoned V₂O₅/WO₃-Ti O₂ catalysts on gaseous elemental mercury oxidation was studied.In addition,regeneration experiments were conducted for potassium poisoning catalysts,and the effects of the regeneration process on the catalysts’NOx and mercury removal activities were explored.The main conclusions are showed below.Firstly,the KCl and K₂SO₄ poisoned catalysts were prepared by the incipient-wetness impregnation method.The catalysts were characterized by X-ray fluorescence（XRF）,Brunner Emmet Teller（BET）,X-ray diffraction（XRD）,Scanning Electron Microscope（SEM）,X-ray photoelectron spectroscopy（XPS）,NH₃-temperature programmed desorption（NH₃-TPD）,H₂-temperature programmed reduction（H₂-TPR）.The results showed that the surface morphology,pore structure and crystal structure of the KCl and K₂SO₄poisoned catalysts surface did not change significantly;XPS test showed that KCl and K₂SO₄ would promote the conversion of V⁵⁺to V⁴⁺on the surface;NH₃-TPD test showed that K would occupy the Br（?）nsted and Lewis acid sites,but SO₄^2-would form strong acidic sites on the catalyst surface;H₂-TPR test showed that the addition of K could reduce the redox properties of the catalyst,whereas SO₄^2-would show strong redox characteristics.Subsequently,the mercury oxidation and NO conversion performance of the poisoned catalysts were tested on a small fixed-bed reactor.When catalysts were poisoned by KCl,the mercury oxidation efficiency would decrease.When low amount of K₂SO₄（3%）was loaded on the catalysts,the oxidation efficiency of Hg⁰ was promoted.However,the oxidation efficiency of mercury would also decrease when>3%K₂SO₄ was loaded.O1s XPS and Hg-TPD results showed that K⁺would occupy the active sites and reduce the adsorption of Hg⁰on the surface,However,Cl^-would be adsorbed on the surface and form V₂O₃（OH）₂Cl₂that was the intermediate specie for Hg⁰ oxidation;SO₄^2-would form new acidic sites on the catalyst surface,and promoted the adsorption of Hg⁰ and the formation of O_ɑon the surface.Finally,the catalysts poisoned by KCl and K₂SO₄ were regenerated by water washing and acid washing（1%,2%）.The BET,XRF,and XPS tests were performed on the regenerated catalysts.The results showed that water washing could only remove a small amount of K on the catalyst surface,and acid washing could remove most of the potassium on the catalyst surface,but at the same time,it also removed some of the active ingredients.The mercury oxidation and NO conversion performance tests illustrated that the KCl poisoned catalyst regenerated by 2%H₂SO₄solution and the K₂SO₄poisoned catalyst regenerated by 1%H₂SO₄solution performed best,but both were not as good as fresh catalyst.Furth research on mercury oxidation mechanism of regenerated catalysts showed that SO₄^2-of wash solution could be deposited on the catalyst surface and form new acidic sites,which would promote the adsorption of Hg⁰ and the formation of O_ɑ.